A Hubble Space Telescope Advanced Camera for Surveys Search for Brown Dwarf Binaries in the Pleiades Open Cluster

ABSTRACT

We present the results of a high-resolution imaging survey for brown dwarf binaries in the Pleiades open cluster. The observations were carried out with the Advanced Camera for Surveys (Pavlovsky and coworkers) on board the Hubble Space Telescope. Our sample consists of 15 bona fide brown dwarfs. We confirm two binaries and detect their orbital motion, but we did not resolve any new binary candidates in the separation range between 5.4 and 1700 AU and masses in the range 0.035-0.065 Msolar. Together with the results of our previous study (Martín and coworkers), we can derive a visual binary frequency of 13.3+13.7-4.3% for separations greater than 7 AU, masses in the range 0.055-0.065 Msolar, and mass ratios in the range 0.45-0.9<q<1.0. The other observed properties of Pleiades brown dwarf binaries (distributions of separation and mass ratio) appear to be similar to their older counterparts in the field.